Dynamic brake for induction motors 

Thanks, James! I am glad to be of helpl!

Thanks, Robert!!

Thanks, George, for your kind comment!!! I invite you to watch my videos on solar energy!! It's amazing most people ignore this wonderful source of energy available to everyone at an incredibly low cost!! Please watch my playlists on solar energy!! I give you FREE step by step instructions on how to install solar power in the home!!

Electric

@@skyscrapersimfantests Yeah, dynamic braking is great for stopping a motor either instantly on a desired ramp. Thanks for your contribution!! If you want to see a physical demo, please go to my video at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html , where I used a car battery to stop a squirrel cage AC motor.

Dear friend, I have other publications on the subject which may help you. One is a braking demo done with a car battery. Another is a homemade timer which can be adjusted for desired braking. Please take a look at.... ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html You can also check at my Community for a simpler system, using a double pole, double throw switch, please go to ru-vid.com/show-UCmjQnuJwV0FkjdEyi3099RAcommunity?lb=UgxNy1n39i1pT2EVCtZ4AaABCQ . If this latte link fails (sometime it does) please go to My Community and find the simple system using a manual switch. Note. This switch has to be normally open when the motor is stopoed.

Thanks, Ali, for your kind comment!!!

Well, yes, but you can adjust the stop for a slower ramp. The idea is not having the flywheel effect have the machinery turning for a long time. It can safely come to a stop in say, ten seconds, without harming the mechanisms.

Dear William, your motor is quite big and requires more DC current to stop it than that provided by a capacitor that size. I would recommend you try this first: Using a car battery perform the experiment I show at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html , being careful to remove the belt (if there is one, or else remove the cutting disk from the chuck, as well as nuts and washers) so the saw chuck does not come apart when suddenly stopping. If the motor stops too quickly, you can add a series resistor to the battery, a relativaly small value, maybe 5 ohms (10 watts or higher) or so, and then try a value which stops the saw at a reasonable rate. Then, you can, with the motor stopped, connect the DC from the battery in series with an ammeter, so you can determine the amps your final DC supply has to be able to handle. Finally, you can build yourself a circuit as shown in my schematic in that same video, just to make sure the DC will be decoupled as soon as the saw stops. Hope this info is of help. Please keep me updated. A word of caution: this method works only for squirrel cage type motors, it won't work for AC-DC motors, aka universal motors.

@@eltunene Gracias, Senor, for that quick and detailed reply. I will watch that video and try your recommendation. I'm pretty sure this is an AC-only motor.

My assumption of 2hp was off - I finally located the spec plate and it says it's a 1hp single-phase motor - does that change the component values by much?

Thank you very much!!

Thanks, D J, for your kind comment!!!

Thank you, corollagl82, for your kind comment!!!

Dear William, I think it would be better to use a much lower resistor, such as 10 ohm and try. Some motors have a very low stator resistance, so the braking current is very low when using a high ohm resistor. If you still don´t get enough braking, please watch a more elaborate circuit at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bKANg7EPMcw.html&t . Nevertheless, I found a really good braking action can be achieved by using a car battery. Then you may try different resistors in order to control the timing; I have a video about that at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html&t . Maybe a NiCad battery can work as well.

@@eltunene I will review the above link. I did look at your video where you demonstrated using a car battery - so I set up a car battery and got the same results. Thank you.

Very stimulating project! I imagine you would have to use a couple of excellent contactors ir order to totally isolate the VFD wiring from the braking circuit to prevent damaging the VFD. You would also have to use a separate variable DC supply so you can play with different DC values to stop the motor gradually enough in order not to submitt any mechanical parts to an excessive effort. DC braking can be very abrupt in stopping the motor if not properly controlled. Inertia of moving parts also plays an important rule in the braking effect. Please take a look at another video in which I used a car battery to stop a 1/3 hp swamp cooler motor. This is the link: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html

You can also add a simple timer to have the DC applied only for about a second or two. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bKANg7EPMcw.html

It's worth trying it!!!

When you apply regen braking to a brush-less DC motor by shorting the motor terminals, (of course, after being disconnected from the switching electronics by means of a double throw suitable relay) you must limit the short-circuit electric current in the motor windings or otherwise the motor may be damaged. A simple way to achieve this is to use braking resistors for each phase. One important factor is the inertia of the motor and load. Try to find a resistor value by trial and error (starting at a relatively high value which just barely reduces the motor speed) and gradually reduce the resistor value until you have the motor stopping after a second or two, or longer if practical. Needless to say, the resistors must be of the proper wattage in order not to overheat.

Chava Tarin thank you. Yes I use a switch relay that disconnect motor from controller and shorten the phases. This is a 350W 36V brushless HUB motor. Will it be possible to add a variable resistor? So I can use the brake from 0% up to 100% .. like a real brake. Guess it will be impossible to find a high Watt variable resistor .

As a matter of fact, you can actually find variable resistors. There are two types I know of: one of them is a long thick resistor, sort of a cigar with resistive wire wound up with one side visible, and an adjustable clamp you can slide and tighten by means of a screw. This is kind of difficult to handle. The other type is sort of a "volume control" rotary type, it is often called a rheostat. You can try with fixed resistors at first and then later buy the proper rheostat based on your maximum value you want to use. In this case, using three rehostats is kind of difficult, unless you link the shafts using some insulating device. Maybe you can adjust the rehostats at a certain value and test until you find your ideal value and have the three rheostars adjusted at a similar position. Sorry for trying to find the simplest solution all the time. I am an old-school technician I guess. ha, ha.

Dear Zack, it surely will, however, being such a large motor, you can use a DC supply, either homemade or factory made. I have a video on that subject on my channel, entitled Squirrel Cage motor braking using a homemade timer.

The link to that video is ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bKANg7EPMcw.html

You will have to modify my circuit in order to accomodate power supplies working on 220. If you wish, give me your e-mail and I could draw you a new schematic for your 3-phase motor. Usually applying DC to one of the phases will provide enough braking action.

Thanks a lot for your interest. As a matter of fact, the circuit explained here is for use in a very small motor, however, I have other videos on the same subject, please take a look at these videos: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bKANg7EPMcw.html also this other one is a demo using a car battery (which can be replaced by a DC power supply): ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html , and this other one is for a demo with a small fan motor: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SEjQHdwgFEY.html Hope this helps.

When the DC from the capacitor or from any DC power supply is applied, the stator coils magnetize and generate an induced current in the squirrel cage short-circuited bars, thus stopping the rotor. As soon as the motor stops, there is no induced current in the rotor, so there is no more braking action, and you can turn it by hand. The braking effect lasts only as long as 1. There is a DC in the capacitor, which discharges almost immediately, and 2 as long as the rotor is turning. So if you use a capacitor, the current magnetizing the stator fades away almost instantly, in case of a big motor, a separate DC supply is used instead of the capacitor, but it applies a current for about a second or two and is disconnected. So after the rotor stops, it can be rotated by hand. The idea of this braking is to overcome the inertia of the load and the rotor itself. As long as this is done, the braking action ceases.

Okay, but how would one stop the rotor from spinning by hand (spinning freely) even when not applying currents to the motor? For instance if you wanted to use a 3 phase AC induction motor on a crane for lifting and lower. How would you stop the lifting wire spool from unwinding and objects being lifted falling to the floor when not applying a current for lifting or lowering?

In that case, you could add an electro-mechanical brake, released by a solenoid when the motor is turned on. Maybe the dynamic brake could help reduce the speed and then the friction brake could hold it. However, in the case of a crane, if the load is very heavy, it would be wiser to apply the friction brake immediately when the motor stops. A mechanical aid can be used such as a wormgear, but for safety I would prefer the mechanical brake.

Dear Anupam, it depends, if the circular saw is of the type built as a workbench, usually they come with a squirrel cage motor. If it is an off-the-shelf handheld portable saw, it almost always uses a universal motor. There are ways to stop a universal motor instantly, but they are usually bulky and impractical. If you have a bench circular saw, its much easier to achieve this. Please give me more info.

@@eltunene Thank you Chava Tarin for your response. The circular saw in question is handled circular saw, eg. Black and Decker CS1500, 220VAC

@@adiyogi453 Unfortunately, these handheld saws use universal motors, and it would be difficult to apply a dynamic braking without disassemblying the unit, at the risk of damaging the commutator and brushes.

Dear Joseph, if the start and stop is too frequent, the capacitor may not get charged enough during the time the motor is stopped. You could experiment by reducing the resistance value a bit. If it becomes too small the diode may short out. If a small resistance value is required, please use higher current diode. Hope that helps!

@@eltunene This is enclosed mechanism in the saw switch, so I cant experiment. From your explanation I understand that if the braking time rises, this means that the resistance of the resistor rose. Is it possible?

Hi, Sam, I kept experimenting and came up with an improved version, lower cost, since the big capacitor needed was too expensive. Please look at schematic at my Community in RU-vid, it is the scheme whose text goes: How to add a timer to dynamic brake - In the figure, SW1 is thrown downwards... I used a couple of inexpensive off-the-shelf power supplies. If your motor is too big, you can build your own power supply with a higher rating. Please take a look at that.

Dear Amul, if a generator is to be used, it would not be a squirrel-cage induction motor. It would rather be an alternator, maybe with a set of diodes (as used in a car) or a parallel wound motor, controlling the field for the amount of power generated. It would require a totally different circuit. By the way, why do you want to stop a benerator dynamically? The load itself tends to stop it, the more the load, the harder it gets to turn the generator.

@@eltunene We are trying to perform an experiment on hydro turbine. The turbine needs to be operated at a fixed speed and the torque that's generated due to water needs to be dissipated somehow. We don't want to use the mechanical brakes for it. We do have a VFD used to turn the induction motor, however it couldn't dissipate more than 25kW.

not sure, but it may be the same, if only one magnetic pole is required

Thanks for your comment!!!

IKR!😂

When applying the DC to the AC motor, you can experiment with several resistors (medium wattage) until you are able to stop it just as you need. I used a car battery and it works well, however, you can find a battery charger or otherwise a DC power supply you can make some modifications to achieve a softer stop. Please watch my video using a car battery, the link is - ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HQssG7woEBY.html . Soft braking is important when the load has delicate components not able to withstand such a sudden stop.

The dynamic brake can be an ideal solution! You can try several values for resistor R2 until it stops as you want it to. If the flywheel is too heavy to stop in a short time, you can add some capacitance, maybe another capacitor in parallel, but you must experiment a bit.

Thanks for the reply. I actually do "NOT" want any braking to happen . you might have read my comment wrong. so can I disconnect the brake ? If I can, how then? Thanks

If the braking is of the spring-applied electromechanical type, you can remove the solenoid-operated brake shoe mechanism some motors have in the end of the shaft, they are usually removable. I hope this helps.

Dear Nishan, no, it is an AC motor. When you apply a DC to the stator, a current is induced in the shorting bars of the rotor, so an opposing magnetic field is produced in the rotor, which reacts with the magnetic field of the stator, thus braking the motor.

Nishan, please watch ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bKANg7EPMcw.html and ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SEjQHdwgFEY.html for more about this dynamic braking. I found out a DC power supply works best instead of a capacitor.

Dear Dan, a squirrel cage motor cannot act as a generator, producing voltage in the stator (field winding), since the rotor (armature) is just a shortcircuited bar group. However, if you apply the charge of the capacitor to the stator while the armature is still rotating, the stator becomes magnetized and a voltage is induced in the rotating bars of the armature. Since they are short-circuited, the strong current generated in the bars produces an opposing field to that of the stator, thus braking the motor. I hope this helps.

Ahh okay, I understand now. Thanks for the input. I was thinking the motor behaves the same as a regular DC motor!

Thanks for your comment! The system can be improved for bigger motors, using a 12 VDC power supply, please watch my demo video on a shaded pole motor being stopped instantly by a small power supply. The supply must be robust enough for big motors, in order to prevent overload of the DC supply - ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SEjQHdwgFEY.html

I have a 1/2 hp ac motor 1 phase 220v. In this motor had a start capacitor 15 uf 400va. I see your circuit have a capacitor, so brake the motor, i need another capacitor like your video ? Waiting for your reply. Thanks !

Hi, Nghia, well yeah, you need another capacitor, however, for motors 1/2 hp and above it is better to use a transformer powered DC supply which is able to get a current through the windings without overheating the xfmr or overloading the diodes. You can use a capacitor, however, it would have to be quite big in order to sustain a heavy curren long enough to stop the motor. Take into account that the voltage used to stop the motor is DC, so the current will be only limited by the ohmic value of the motor windings, so if the ohmic resistance of the motor is very low, the current will be quite high, so the DC supply must be capable of handling the braking current long enough to stop the motor, load inertia and all. You have to try several DC supplies, starting with a low voltage, perhaps 6V and if that is enough to stop the motor, use the minimum current necessary.

Watch this video in which I apply voltage from a small power supply in order to stop a small shaded pole motor. It will give you an idea of how fast can a motor be stopped by applying DC to the windings. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SEjQHdwgFEY.html

Thank you very much. I did it :D. Very happy. Thanks !

Dear Nhan, as a matter of fact, I found using an offshelf DC power supply works practically in all cases (except very big motors) I show a demo of the components needed at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SEjQHdwgFEY.html . If the motor is over 100 W, you may have to devise a somewhat stronger power supply, capable of delivering a 2 or 3 amps for a short period. You must provide some sort of timer or momentary button to apply the brake, so the power supply will not overheat. You can use a "breadboard" with plywood and nails as I did in order to make some tests and find the proper supply. You can check the ohms resistance of the motor when not energized, to have an idea of the amount of current your supply must be able to deliver. Please let me know what you finally did.

@@eltunene thank you so much for your reply.!! you know, i have a AC motor 1 phase. (110 v, 50w), which have a start winding and 1 capacitor. so, i want make a circuit to brake the motor when i turn off. but i don't know what i have to do. i am wondering, can i apply your circuit in my motor?

Your motor is small enough, The circuit in my video should do fine, however, I later found out it was easier to use a small power supply. Maybe you can use a small relay and capacitor as a timer to apply the brakes for a second or two. Please go to my Community where I posted a schematic.

@@eltunene thank you so much!! but i have applied your circuit for my motor already. but it seem less effective. please give me the way to receive your schematic

@@classicmotorcycle136 There is a tab in youtube labeled Community, where I have posted a couple of pictures. One of them is about the braking circuit. I make use of a relay and a delay circuit using an electrolitic capacitor in order to apply the brake just for a second or two (that depends on the capacitor in this circuit) please refer to that picture. In case you do not find it, please give me an e-mail so I can send you the pix.

GURUMAHARAJ earth is flat, let India know